With the recent popularization of computers, inkjet printers are much used for printing on paper, films, cloths and others, not only in office work but also for home use.
The inkjet recoding method includes a system of applying pressure to ink drops by the use of a piezoelectric device to thereby make the ink drops jet out, a system of thermally bubbling ink to jet the ink drops, a system of using ultrasonic waves, and a system of sucking and jetting ink drops by electrostatic force. For the ink compositions for such inkjet recording, usable are aqueous inks, oily inks and solid (hot-melt) inks. Of those, aqueous inks are most used because of their productivity, handlability, odorlessness and safety.
Colorant to be used in such inkjet recording inks must satisfy the following requirements: Its solubility or dispersibility in solvent is good; it enables high-density recording; its hue is good; it is fast to light, heat, air, water and chemicals; it well fixes in image-receiving material and hardly bleeds out; its storage stability in inks is good; it is not toxic; its purity is high; and it is inexpensive and is readily available. However, it is extremely difficult to seek such colorant that satisfies all these requirements on a high level. Various dyes and pigments have been already proposed for inkjet, and are now in practical use. At present, however, no one knows colorant that satisfies all the requirements. Dyes and pigments heretofore well known in the art such as those listed in Color Index (C.I.) could hardly satisfy both the color hue and the fastness, which inks for inkjet need.
The inventors have studied a high performance ink having both the color hue and the fastness, relating to and ink for inkjet containing a dye. In such study, the inventors found that storage stability of images become lower when aqueous inks are used, and particularly, aqueous inks have week to humidity and deteriorations of image come about when stored in high-humidity, because of dye-movement. Further, inks for inkjet may cause beading or bronzing as they may aggregate and crystallize on image-receiving material, and this is problematic since it lowers the image quality. In addition, inks are desired to have good jet-out stability through nozzles.